bit chapter4
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ITEC 1010 Information and Organizations
Chapter 4
Linking Info. Tech.
ITEC 1010 Information and Organizations
Communications
Communications
The message (data and information) is
communicated via the signal
The transmission medium carries the signal
Sender ReceiverSignal
Transmissionmedium
ITEC 1010 Information and Organizations
Communications Discussion
The transmission of data from one computer to another, orfrom one device to another. A communications device,
therefore, is any machine that assists data transmission. For
example, modems, cables, and ports are all communications
devices. Communications software refers to programs that
make it possible to transmit data.
ITEC 1010 Information and Organizations
Telecommunications
Telecommunications
The electronic transmission of signals for
communications, including such means as:
Telephone
Radio
Television
Telecommunication medium Anything that carries an elec tronic signal and interfaces
between a sending device and a receiving device
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ITEC 1010 Information and Organizations
Communications andTelecommunications
In human speech, the sender transmits a signal throughthe transmission medium of the air
In telecommunications, the sender transmits a signalthrough the transmission medium of a cable
Schematic
ITEC 1010 Information and Organizations
ITEC 1010 Information and Organizations
Data Communications
Data communications
A specialized subset of telecommunicationsthat refers to the electronic collection,processing, and distribution of data -- typically
between computer system hardware devices
ITEC 1010 Information and Organizations
Elements of a
Telecommunications System
Telecommunication devices
Relay signals between computer systems andtransmission media
Schematic
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ITEC 1010 Information and Organizations ITEC 1010 Information and Organizations
Computer Network
Computer network
The communications media, devices, and
software needed to connect two or morecomputer systems and/or devices
Used to share hardware, programs, anddatabases across the organization
Fosters teamwork, innovative ideas, and new
business strategies
ITEC 1010 Information and Organizations
Speed of Communications BPS
In telecommunications and computing, bit rate ordata rate is the number of bits that are conveyed or
processed per unit of time.
The bit rate is quantified using the 'bits per second'
(bit/s or bps) unit, often in conjunction with a SI
prefix such as kilo- (kbit/s or kbps), mega-(Mbit/s or
Mbps), giga-(Gbit/s or Gbps) or tera (Tbit/s or Tbps).
ITEC 1010 Information and Organizations
Types of communications Media
Twisted pair wire cable Insulated pairs of wires historically used in
telephone service and to connect computerdevices
Coaxial cable Consists of an inner conductor wire
surrounded by insulation, called the dielectric
The dielectric is surrounded by a conductiveshield, which is surrounded by a non-conductive jacket. Coaxial cable has betterdata transmission ra te than twisted pair
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ITEC 1010 Information and Organizations
Types of communications Media
Fiber-optic Cable Many extremely thin
strands of glass or plasticbound together in asheathing whichtransmits signals withlight beams
Can be used for voice,data, and video
ITEC 1010 Information and Organizations
Other types ofTelecommunications Media
Microwave Communications
Satellite transmission
Cellular transmission
Infrared transmission
Pretty picture
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Terminology
Analog Signal
A continuous, curving signal
Digital Signal
A signal represented by bits
Modems
Devices that translate data from digital to
analog and analog to digital
ITEC 1010 Information and Organizations
Analog /Digital
Almost everything in the world can be described or representedin one of two forms: analog or digital. The principal feature ofanalog representations is that they are continuous. In contrast,digital representations consist of values measured at discreteintervals.
Digital watches are called digital because they go from onevalue to the next without displaying all intermediate values.Consequently, they can display only a finite number of times of
the day.
ITEC 1010 Information and Organizations
Analog Discussion (1)
In contrast, watches with hands are analog, because the hands movecontinuously around the clock face. As the minute hand goes
around, it not only touches the numbers 1 through 12, but also the
infinite number of points in between.
Early attempts at building computers used analog techniques, but
accuracy and reliabili ty were not good enough. Today, almost all
computers are digital.
Analog /Digital
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ITEC 1010 Information and Organizations
Digital Discussion (1)
Describes any system based on discontinuous data or events.
Computers are digital machines because at their most basic levelthey can distinguish between just two values, 0 and 1, or off andon.
There is no simple way to represent all the values in between, suchas 0.25. All data that a computer processes must be encodeddigitally, as a series of zeroes and ones.
The opposite of digital is analog. A typical analog device is a clockin which the hands move continuously around the face. Such aclock is capable of indicating every possible time of day. Incontrast, a digital clock is capable of representing only a finitenumber of times (every tenth of a second, for example).
Analog /Digital
ITEC 1010 Information and Organizations
In general, humans experience the world analogically. Vision, forexample, is an analog experience because we perceive infinitelysmooth gradations of shapes and colors.
Most analog events, however, can be simulated digitally.Photographs in newspapers, for instance, consist of an array ofdots that are either black or white.
From afar, the viewer does not see the dots (the digital form), butonly lines and shading, which appear to be continuous.
Although digital representations are approximations of analogevents, they are useful because they are relatively easy to store andmanipulate electronically.
The trick is in converting from analog to digital, and back again.
Analog /Digital
ITEC 1010 Information and Organizations
This is the principle behind compact discs (CDs). The musicitself exists in an analog form, as waves in the air, but thesesounds are then translated into a digital form that is encodedonto the disk.
When you play a compact disc, the CD player reads the digitaldata, translates it back into its original analog form, and sends itto the amplifier and eventually the speakers.
Internally, computers are digital because they consist of discreteunits called bits that are either on or off. But by combining
many bits in complex ways, computers simulate analog events.
In one sense, this is what computer science is all about.
Analog /Digital
ITEC 1010 Information and Organizations
How a Modem Works
Modem
Modulates a digital signal into an analog signalfor transmission via analog medium, thendemodulates the signal into digital for receiving
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ITEC 1010 Information and Organizations
Modem Acronym for modulator-demodulator. A modem is a device that
enables a computer to transmit data over telephone lines.
Computer information is stored digitally, whereas informationtransmitted over telephone lines is transmitted in the form ofanalog waves. A modem converts between these two forms.
Fortunately, there is one standard interface for connecting
external modems to computers called RS-232. Consequently,
any external modem can be attached to any computer that hasan RS-232 port, which almost all personal computers have.
There are also modems that come as an expansion board that
you can insert into a vacant expansion slot. These are
sometimes called onboard or internal modems.
ITEC 1010 Information and Organizations
Multiplexer
Multiplexer
Allows several telecommunications signals to
be transmitted over a single communicationsmedium at the same time
ITEC 1010 Information and Organizations
Carriers and Services (1)
Carriers Organizations that take the responsibility of ensuring telecommunications
can effectively take place between enterprises
Common carriers Long-distance telephone companies
Value-added carriers Companies that have developed private telecommunications systems and
offer their services for a fee
Switched lines Lines that use switching equipment to allow one transmission device to
be connected to other transmission devices (e.g., standard telephone line)
Dedicated line A line that provides constant connection between two po ints. No
switching or dialing is needed
ITEC 1010 Information and Organizations
Carriers and Services (2)
Private branch exchange (PBX)
Communication system that can manage both voice and data transfer
within a location (e.g. a building) and to outside lines
Wide area telecommunication service (WATS)
Billing method fo r heavy users of voice services
Phone and dialing services
Includes automatic number identification (a.k.a. caller ID)
Integration of telephones and personal computers
Access code screening
Call priorities
One number portability (use anywhere)
Intelligent dialing (auto re-dial for a busy number)
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ITEC 1010 Information and Organizations
ISDN ISDN = Integrated Services Digital Network
Technology that uses existing common-carrier linesto simultaneously transmit voice, video, and image
data in digital form
Pretty picture
Carriers and Services (3)
ITEC 1010 Information and Organizations
ITEC 1010 Information and Organizations
T1 carriers An expensive service developed by AT&T to
increase the number of voice calls that could be
handled through existing cables
Digital subscriber lines (DSL) Uses existing phone wires going into todays homes
and businesses to provide transmission speeds
exceeding 500 Kbps at a cost of $100 - $300 per
month
Carriers and Services (4)
ITEC 1010 Information and Organizations
Networks and Distributed
Processing
Centralized processing Data processing that occurs in a single location or
facility
Decentralized processing Data processing that occurs when devices are placed at
various remote locations
Distributed processing Data processing that occurs when computers are
placed at remote locations but are connected to eachother via telecommunications devices
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ITEC 1010 Information and Organizations
Network Topology
Network Topology A logical model that describes how networks
are structured or configured
Topologies
Ring Bus Star Hybrid
ITEC 1010 Information and Organizations
Switch/Hub
Start topology links the computers by individual cables to a
central unit, usually a hub. When a computer or other
networking component transmits a signal to the network,
the signal travels to the hub.
Then, the hub forwards the signal simultaneously to all
other components connected to the hub. Ethernet 10BaseTis a network based on the star topology. Star topology is the
most popular way to connect computers in a workgroup or
departmental network
Network Topology
ITEC 1010 Information and Organizations
Ring A ring topology connects the computers along a single path
whose ends are joined to form a circle.
The ring topology is commonly used in token ring networks
that the ring of a token ring network is concentrated inside a
device called a Multistation Access Unit (MAU) and fiber
Distributed Data Interface (FDDI) networks that the ring in thiscase is both a physical and logical ring and usually runs around
a campus or collection of buildings to form a high-speed
backbone network.
Network Topology
ITEC 1010 Information and Organizations
Bus A bus topology connects computers along a single or more
cable to connect linearly as figure 1. A network that uses a bus
topology is referred to as a "bus network" which was the
original form of Ethernet networks. Ethernet 10Base2 (also
known as thinnet) is used for bus topology
Network Topology
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ITEC 1010 Information and Organizations
Hierarchical Uses treelike structures
with messages passedalong the branches of the
hierarchy
Hybrid Network made up of
various types oftopologies
Network Topology
ITEC 1010 Information and Organizations
Network Types
Local area network (LAN) Connects computer systems and devices in the same
geographic area (can be Ring, Bus, Hierarchical, Star,Hybrid)
Wide area network (WAN) Ties together large geographic regions using
microwave and satellite transmission or telephonelines
VAN Network provide additional services such as games,
fax, phone etc.
ITEC 1010 Information and Organizations
File Server Connection
Applications and databases reside on the samehost computer
File server transfers data and programs to PCs
on the network, where these target PCsperform most of the processing
Host
computer
File downloadedto user
File server
Target PC
ITEC 1010 Information and Organizations
Client/Server Connection
Applications and databases reside onspecialized host computers
Servers do most or all of the processing andtransmit the results to the client
Client Server
Server ServerClient
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ITEC 1010 Information and Organizations
Adv. & Disadv. of Client/Server
Advantages Reduced cost potential
Improved Performance
Increased Security
Disadvantages Increased cost potential
Loss of control
Complex multi-vendor
environment
ITEC 1010 Information and Organizations
Network Applications
Linking personal computers to server computers Download and upload information
Voice mail Enables users to leave, receive, and store verbal
messages for and from other users
Electronic mail (e-mail) Enables a sender to connect a computer to a network,
type messages, and send it to another person on thenetwork
ITEC 1010 Information and Organizations
Electronic software distribution Involves installing software on a file server for users to share
by signing onto the network and requesting that the softwarebe downloaded onto their computers over a network
Electronic document distribution Transporting documents -- such as sales reports, policy
manuals, and advertising brochures -- over communications
lines and networks
Telecommuting Enables employees to work away from the office using
personal computers and networks to communicate viaelectronic mail with other workers and to pick up and deliverresults
Network Applications
ITEC 1010 Information and Organizations
Videoconferencing
Allows participants to conduct long-distancemeetings face to face while eliminating
Pretty picture
Network Applications
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Electronic Data Interchange (EDI) Uses network systems and follows standards and
procedures that allow output from one system to be
processed directly as input to other systems, withouthuman intervention
EFT Electronic Fund transfer service sending money online
to other accounts. To may utility bills, other online
payments, payment using Credit card.
Pretty picture
Network Applications
ITEC 1010 Information and Organizations
EDI link
EDI link EDI link
Vendor Customer
Vendor Customer
Third-partyclearing house
(a)
(b)
ITEC 1010 Information and Organizations
Public network services
Services that give personal computer users access to vast
databases and other services, usually for an initial fee
plus usage fees
Specialized and regional information services BBS
Specialized electronic bulletin boards and e-mail services
targeting particular interests.
Distance learning
Use of telecommunications to extend the classroom
Network Applications